1. Technical Field
The present invention relates to an optical signal modulator for an optical communication system, and more particularly to an optical waveguide intensity modulator utilizing a poling effect of non-linear polymer and optical bireferingence and an electro-optic effect induced from the poling effect.
2. Description of the Related Art
For an optical communication system, a number of optical devices, for example light emitting devices, light receiving devices for detecting a light, and optical signal processors for accomplishing optical switching and modulation operation are required. The optical switching devices and optical modulation devices utilizing an electro-optic effect can modulate optical signals by applying an electric field to materials, such as LiNbO.sub.3, GaAs, InP, polymer, etc, having nonlinear electro optical characteristics. In such devices, the optical devices using LiNbO.sub.3 or GaAs have been mainly developed and used in commercial optical communication systems.
An optical waveguide intensity modulator (hereinafter, referred to as an intensity modulator) is widely used in modulating the optical signal intensity on the outside of a light source, such as a diode laser, so that an optical signal suitable for using in optical communication may be generated. Conventionally, an optical signal modulator has been disclosed in a waveguide structure of a Mach-Zehnder interferometer. Such a modulator is known from an article: .sup..left brkt-top. C. C. Teng, "Travelling-wave optical intensity modulator with more than 40 GHz of 3 dB electrical bandwidth", Appl. Phys. Lett. vol. 66, pp. 1538-1540, 1992.sub..right brkt-bot.. In the known art, the intensity modulator comprises a curved part of a waveguide, and a Y-branch coupler for dividing and combining a propagating light at the ratio of 50 to 50. After the light that has been split into two arms with the same polarization directions is coupled back together after passing through different optical paths, the intensity of the coupled light is modulated by constructive inteference or destructive interference of the isolated lights according to their phase difference. However, in the Y-branch coupler and the curved part there may be a lot of light loss. Moreover, in order to reduce this loss, careful attention must be paid to the design and fabrication process for the arms of the Mach-Zehnder interferometer waveguide.